1. Field of the Invention
The present invention relates to position sensing mechanisms and methods including mechanisms and systems for determining the position of members such as railroad switch points. More particularly, the present invention concerns a vital proximity detection mechanism and method for reliably determining and communicating the position, e.g., normal or reverse, of railroad switch points relative to one or more fixed tracks, wherein the mechanism includes substantial component redundancy and fault-checking features and otherwise meets promulgated safety standards for vital componentry.
2. Description of the Related Art
It is often necessary to direct trains from one track onto another. This is accomplished with a switch comprising a pair of movable rails with tapered ends or switch points. The switch points are selectively moveable between a pair of stock rails to direct the train toward one of two diverging tracks or vice versa. The switch points may referred to as “normal” and “reverse” switch points and may be described as being advanceable between a “normal” position and a “reverse” position.
When in the “normal” position a first or normal switch point is positioned against a first stock rail and a second or reverse switch points is advanced away from the second stock rail. In the “reverse” position, the reverse switch point is advanced against the second stock rail and the normal switch point is advanced away from the first stock rail. With the normal switch point in the “normal” position, the flange on the rail car wheels traveling along the first stock rail will advance inside of the normal switch point and onto the switch rail associated with the normal switch point and the flanges on the rail car wheels on the second stock rail will pass between the reverse switch point and the second stock rail and remain on the second stock rail, thereby directing the rail cars toward a first or normal section of track. With the switch in the “reverse” position, the flange on the rail car wheels on the second stock rail will travel inside of the second switch point and onto the switch rail associated with reverse switch point while the rail car wheels on the first stock rail will pass between the first switch point and the first stock rail and remain on the first stock rail, thereby directing the rail cars toward a second or reverse section of track.
It is extremely important that the switch points be aligned with the proper track within prescribed safety tolerances or the train may immediately derail. Furthermore, it is extremely important that the actual and true position, whether normal or reverse, of the switch points be determined and communicated because the two fixed tracks may require very different maximum safe travel speeds to avoid subsequent derailment. Thus, for example, a train may expect the switch point to be in a normal position and therefore to proceed onto the main track, only to discover that the prior art switch point position detection mechanism is malfunctioning and the train is, in fact, moving onto the branch track at an unsafe speed which may cause it to derail.
It is generally known to use a switch circuit controller for determining the position of the switch point. These prior art mechanisms typically meet the standards or specifications promulgated by the American Railway Engineering and Maintenance-of-Way Association (AREMA) for “vital” components or devices, i.e., components or devices whose function affects the safety of the train, such as certain signal lights, relays, switches, and circuits.
However, these prior art switch point position detection mechanisms suffer from a number of other problems and disadvantages that can cause a loss of detection or an inaccurate indication of switch point position, the consequences of which include increased maintenance costs and increased risks of train delays or derailments. These problems and disadvantages include, for example, loose or worn connecting rod linkages; loose or worn bolts or screws that fasten the prior art controller box to the ties or plates; worn bearings, connections, or contacts in the prior art controller box; improper adjustment of cams, contacts, and linkages; shorted, open, or crossed wirings due to mechanical damage, rodent damage, and various other causes; running rails; and labor-intensive installation maintenance, inspection, and adjustment requirements.
Due to the above-identified and other problems and disadvantages in the prior art, a need exists for an improved mechanism or method for more reliably determining and communicating the position and alignment of a railroad switch point.